Surface water run-off is coming under increased scrutiny as a source of pollutants entering ground water, streams and rivers. As water from rain or snow melt and other sources flows over the surface of the ground it picks up a wide variety of pollutants, ranging from large and small debris, suspended solids and sediment to oils and other soluble and insoluble chemical contaminants. Because surface water is relatively easily contained through storm sewers and dry wells, many agencies at all levels of the government are paying increased attention to both the contaminants that enter the water system through surface water run-off, and to methods to control and eliminate such contaminants. Moreover, governmental regulations currently in place put restrictions on the amount of sediment that can be permitted to flow into sewer systems.
A municipal storm sewer system is one type of traditional surface water filtering system. In this type of system a series of catch basins or collection boxes are interconnected with sewer pipe. Surface water flows into the catch basin, often a relatively narrow un-grated inlet opening—the opening is often 4 inches or less in height. The water that flows into the opening enters the catch basin, which is a collection box or vault that functions essentially as a settling basin. Such collection boxes are sometimes called sump tanks. Some sediment that flows into the system settles to the bottom of the basin, and the water flows through an outlet pipe and into the sewer system and, depending upon the system, either to another processing facility or directly into a stream or river.
This traditional system is useful as a primary control system, and is relatively inexpensive, but it has many problems. As examples of the problems, the catch basin can quickly be filled with sediment if the water contains a high level of solids or sediment, causing the catch basin to become filled and the system to overflow or become clogged. Because the catch basin is typically a cylindrical tube or a rectangular box that sits below grade level, cleaning the sediment out of the basin can be a difficult job. Cleaning is made much more difficult if the system is clogged and the basin is underwater. Just as important, the system does not stop all of the sediment and other pollutants in the run-off. Typically, the water flow through the basin is fairly turbulent, especially when there is a lot of water flowing through the system, for instance during a storm. When this occurs very little sediment settles out, and is instead washed through the basin and into the sewer system. This may result in non-compliance with governmental regulations, possibly resulting in fines. Finally, a typical catch basin system does nothing to collect oils and other chemical contaminants and dissolved solids.
The grated catch basin type of system is routinely used with both private and municipal systems. In a dry well the surface water that flows through the sump tanks flows into a dry well associated with one or more basins rather than flowing into a municipal or other sewer system. However, to function properly, dry wells must have sufficient flow-through characteristics. Water containing a high level of sediment can quickly clog a dry well by stopping water flow-through. And as noted above, a grated catch basin does not stop oils and other chemicals. These kinds of pollutants, and especially oils that flow through the system can clog dry wells very quickly. Commercial dry wells can be very large, especially if they are used to contain run-off from a large area such as a large private parking lot, and are connected to numerous catch basins. It is typically very expensive to dig a new dry well, or to unclog an existing well.
As noted, many government agencies are paying increased attention to contaminants that are carried into streams and rivers in surface water run-off. Because polluted surface water run-off can be a significant source of pollution, agencies have begun to monitor the levels of contaminants in run-off, both in municipal and private systems. In the past several years, many municipalities have begun to impose fees on catch basin users, whether the catch basin is connected to a storm sewer system or a dry well. While these fees apply in most instances to commercial users, they can also apply to residential systems. In large part the fees are based in some manner on the kind and amount of pollutants that flow through the catch basin and into the system. In general, the higher the level of contaminants flowing through the system, the higher the fee. In some cases the amount of the fee is based on the kind of contaminant. For example, oils flowing into a sewer or dry well can lead to increased fees. These fees even apply to private commercial dry well users, since it is in the interest of a municipality to control the amount of pollution that enters the ground water.
There is therefore a strong incentive to decreasing both the amount and kind of contaminants flowing through a catch basin and into either a municipal sewer system or a private dry well or sewer system. First, there is an obvious environmental incentive: by decreasing contamination of all kinds from surface water run-off, the water that flows back into the ground and into streams and rivers is cleaner. This helps to improve environmental conditions in numerous ways. Second, there is a strong economic incentive: when sewer system and dry well users are paying fees based on the amount and kind of contaminants that flow into their systems, it is of obvious advantage to minimize all contaminants. Further, the costs associated with either cleaning catch basins or reconditioning dry wells are substantial. Avoiding or delaying those costs by reducing the amount of contaminants flowing through the system can save substantial amounts of money.
Curb-inlet catch basins are ubiquitous and are one type of vault used in storm sewer systems and functions the same as the systems described above. However, a curb-inlet catch basin is located along side roadways, typically those that are either paved with asphalt or which are concrete. Water flows off the roadway and enters the catch basin through an opening formed in a roadside curb. While there are numerous different designs for curb-inlet systems, a typical system has a below-grade vault made of reinforced concrete and which is connected to the sewer system through pipes. The vault is generally a square or rectangular box, the upper edge of which is typically at or near the same elevation as the roadway. A square riser or lid that is the same size as the vault and which also is typically concrete sits atop the vault. The riser is typically the height of the curb. A top unit typically sits atop the riser and defines a plate that rests on the riser and covers the vault. The top unit has a removable manhole cover, almost always round, which allows access to the vault for maintenance. Often, the lid is a one piece unit that covers the vault and has a manhole that provides access to the interior of the vault.
Curb-inlet systems present the same problems as the other systems described above and it is therefore desirable to filter water that flows into the systems. However, curb-inlet systems present unique challenges since the manhole access covers are typically round and the vaults beneath the covers are typically square and because the lid that covers the vault typically cannot be removed once it is in place, at least not without a significant amount of work involving equipment able to lift very heavy concrete structures (i.e., the lid). And in cases where the manhole access cover is other than round, the access plate to the underlying structures is typically smaller in size than the vault below the access plate. It is very difficult therefore to retrofit a filter system that easily fits through the round manhole cover and securely attaches to the vault. As a result, installation of conventional filtering systems is made very difficult; often the entire top unit has to be removed and a significant amount of labor is required to install the filter system.
There is a need therefore for a filter system that may be easily installed in existing curb-inlet catch basins.